This invention relates to sound reducing baffles for use with air-cooled induction apparatus such as an electrical transformer. The use of power transformers operating in the kilovolt range inside residential and commercial buildings may present a noise problem.
In ventilated dry type transformers, the transformer assembly is cooled by natural convection currents or by forced air cooling. Ventilating openings are provided near the top and bottom of the enclosures in order to permit the free passage of air to the transformer during the cooling process. In order to reduce the amount of noise radiated from the transformer enclosure, the inner walls of the enclosure are frequently lined with a sound absorbing material. Since the housing is essentially sealed except for the ventilating openings, and since it has been heretofore impossible to baffle the sound emanating through the ventilating openings without interfering with the flow of air necessary to cool the transformer, they are the main sound transmission path.
One method for attempting to reduce the sound generated within an air ventilated dry type transformer is described in U.S. Pat. No. 3,451,503. This method provides a Helmholtz resonator mounted within the transformer enclosure proximate each of the ventilating openings. The sound, in passing through the ventilating openings, becomes attenuated to some degree since the resonator cavities are tuned to the frequency of the generated sound. Each of the Helmholtz resonators is mounted adjacent each ventilating opening and particular care is taken not to restrict the ventilating opening.
The increasing use of power transformers in residential localities anticipates a further reduction in the amount of noise emanating from the transformer enclosure. The transformers can generate sound in excess of 60 dBA and it has been determined that sound levels in excess of 45 dBA can be uncomfortable, especially in the evening. The purpose of this invention therefore is to provide sound attenuating apparatus for use with dry type, air cooled electrical apparatus to effectively reduce the level of the transformer generated sound with little or no interference with the transformer cooling process.